package Text6;
import java.util.*;
public class Main {

    public static int N = 150010, n, m, idx;
    public static int[] h = new int[N];
    public static int[] e = new int[N];
    public static int[] ne = new int[N];
    public static int[] w = new int[N];
    public static int[] d = new int[N];
    public static boolean[] st = new boolean[N];

    public static void add(int a,int b,int c){
        e[idx]=b;
        ne[idx]=h[a];
        w[idx]=c;
        h[a]=idx++;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        n = scanner.nextInt();
        m = scanner.nextInt();
        Arrays.fill(h,-1);
        Arrays.fill(d,Integer.MAX_VALUE);
        d[1]=0;
        for (int i = 0; i < m; i++) {
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            int c = scanner.nextInt();
            add(a,b,c);
        }
        System.out.println(dijkstra());
    }

    private static int dijkstra() {
        PriorityQueue<PII> p = new PriorityQueue<>();
        p.offer(new PII(0,1));
        while (p.size()>0){
            PII t=p.poll();
            int ver = t.b, distance = t.a;
            if(!st[ver]){
                st[ver]=true;
                for (int i = h[ver]; i!=-1 ;i=ne[i]) {
                    int j=e[i];
                    if(d[j]>distance+w[i]){
                        d[j]=distance+w[i];
                        p.offer(new PII(d[j],j));
                    }
                }
            }
        }
        if(d[n]==Integer.MAX_VALUE){
            return -1;
        }else {
            return d[n];
        }
    }
}

class PII implements Comparable<PII>{
    int a;//距离值
    int b;//点编号

    public PII(int a, int b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public int compareTo(PII o) {
        return Integer.compare(a,o.a);
    }
}
